A NATION CHALLENGED: AIRPORT SECURITY; Deadline for Bomb Screening Will Not Be Met

The Transportation Department said today that it would not meet the Dec. 31 deadline Congress had set for screening all baggage checked at the nation's airports with costly explosive detection systems.

Instead, Norman Y. Mineta, the secretary of transportation, said the agency would use the machines in combination with trace detection systems, which are already familiar to travelers who carry hand luggage, and manually operated scanners.

The decision may set off a struggle with Congress, where some leaders are eager to preserve the original requirements of the security bill.

Mr. Mineta said that meeting Congress's preference was not practical. Only two companies now produce the explosives detection system machines and, he said, they lacked ''the capacity to be able to provide all the machines we need.''

Experts say that about 2,200 machines, known as E.D.S. machines, are required. The machines are as big as a minivan and considerably heavier; they sometimes require rebuilding sections of airports to install, and some cost more than $1 million each.

Mr. Mineta said that department officials were meeting with companies that could produce components or entire machines under license. Another possibility, he said, was to build machines that would scan bags and display the results to a human operator.

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The E.D.S. machines use a computer to scan the bag, because of concerns that a human operator might miss signs of a bomb. But Mr. Mineta said that the agency would hire and train better screeners and will supervise them better.

The department is supposed to report to Congress on its ''deployment plan'' on May 18, and may find part of its plan a hard sell.

''We want them to meet this deadline,'' said a senior Senate staff member. The law gives the department an alternative to the 100 percent E.D.S. plan, but is intended only as an interim alternative.

The trace detection systems are in common use now at checkpoints where guards inspect hand-carried items. A screener runs a cloth pad over the exterior of the item and puts it in an analyzer, which looks for signs of explosives.

The two E.D.S. machine manufacturers are InVision Technologies of Newark, Calif., and L-3 Communications of New York. When the airlines ran security, they did not like either machine, especially the L-3 model because, they said, it often broke down. The company said the problem was fixed.